The present invention relates generally to exhaust systems for aircraft gas turbine engines, and in particular to an exhaust nozzle capable of completely blocking flow of exhaust gas.
Advanced short takeoff and vertical landing (STOVL) aircraft must operate effectively over a wide range of flight conditions, including conventional forward flight and vertical or hovering flight. Those conditions impose special requirements on exhaust nozzles. In forward flight, a nozzle must efficiently accelerate high pressure exhaust gas in a generally horizontal direction to generate forward thrust as the gas exits from an aft end of the aircraft. In vertical flight, the nozzle should prevent exhaust gas from exiting horizontally, instead directing it vertically downward to generate lift.
The nozzle typically includes flaps defining a convergent upstream duct leading to a plane of minimum flow area known as a throat, and a divergent downstream duct extending from the throat to an exit. The nozzle also includes a mechanism for moving the flaps so that the throat and exit may be varied in size to provide for efficient engine operation at all engine power settings, flight speeds, and altitudes. The flaps are constructed to withstand exposure to high pressure and high temperature exhaust gas in a highly vibratory environment. Most nozzle flaps have a liner, a thin metallic shell designed to tolerate high temperatures extending parallel to and adjacent the flap. A layer of cooling air is typically provided between the liner and the flap. The liner may include one or more coating of a material that reduces radar or infrared visibility or enhances the thermal protection of the liner.
Current exhaust nozzles have not been capable of completely preventing all exhaust flow from exiting through the nozzle. Conventional flaps cannot close the nozzle without causing damage because the liners, coatings, and flap structures are typically fragile and easily broken. Any leakage of exhaust gas through the nozzle reduces potential lift and degrades aircraft performance and payload. Therefore, it is critical that all exhaust gas be blocked. Consequently, some aircraft have a separate blocker device, such as a deployable clamshell, in the exhaust system to completely block flow. These devices add substantial weight and complexity to the exhaust system.
In general, an exhaust nozzle of the present invention is for an aircraft engine. The nozzle comprises a mount for attaching the exhaust nozzle to a downstream end of the engine, and first and second opposed upstream flaps moveably connected to the mount having inner surfaces defining an upstream exhaust gas flowpath. Each upstream flap extends between an upstream end and a downstream end and is moveable relative to the mount between an open position in which the downstream ends of the upstream flaps are spaced by a first distance, and a closed position in which the downstream ends touch to substantially block flow through the exhaust gas towpath. First and second opposed downstream flaps are moveably connected to the first and second upstream flaps. The downstream flaps have inner surfaces defining a downstream exhaust gas flowpath.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.